Rare-Earth—Conduction Electron Interaction in 4d and 5d Laves Phases Compounds

Abstract

A systematic investigation has been made of the sign and magnitude of the g shifts of Gd impurities in the AB₂ intermetallic Laves phase compounds. Gd was partially substituted in the A site for the elements Sc, Y, La, Th, U, and Zr. The B sites are occupied by elements of the 4d and 5d group whose positions in the periodic table are such as to correspond to an almost filled d band (e.g., Ru, Os, and Rh). Negative Gd g shifts, Δg, up to 7% were observed; the highest was that found in LaRu₂. It was found that the closer a B element was to having a filled d shell the larger was the g value. It appears, in keeping with our previous EPR measurements on Gd in Rh‐Pd, Pd‐Ag alloys and in Cu₅Ca intermetallic compounds, that without exception the g shifts are negative when the d band is nearly filled in the host alloy and that the g value has a minimum as a function of the atomic position in the host d band metal. In very fine powders of the hard superconductors (Ce_0.99Gd_0.01) Ru₂ and (Th_0.99Gd_0.01) Ru₂ no change in the Gd g shift was observed in going from the normal to the superconductor state. For the superconductor (La_0.15Ce_0.85) Ru₂ the La Knight shift was also observed not to change in going from well above to well below the superconducting transition temperature. In both experiments Ho≪the upper critical field.